I have a jdm Sohc zc block with a y8 head and y8 distributor. I’m not getting any codes. It won’t rev past 4k. I have no idea where to go from here. Everything seems right.

The car is converted to obd1

i wondered if not having any form of cps could be the issue? As I’m using a y8 dizzy. As I know the obd1 dizzy has a cps in the dizzy

 

If not having any form of cps (Crankshaft Position Sensor?) I'd say yes.

My wife's '93 Civic EX (VTEC-OBD1-D16Z6 Engine's Crankshaft Positioning Sensor (CPS) went bad inside her distributor and the car would not go past 3000 rpms without going into limp mode and acted like as if it had a rev-limiter killing out one cylinder.
It took a long time for me troubleshooting trying this or that on the car until I found a resistance check on the CPS inside the distributor from a Haynes manual that failed the test. I replaced the distributor's CPS sensor and the car has run great since.

Your car without having any form of CPS may be causing your limited rpm range issue.

 

The CKP (Crank Position Sensor) is located inside the Civic distributor regardless of whether it is an OBD-2 or OBD-1 type... you are confusing the additional sensor found on OBD-2 Civics around the crankshaft called the CKF (Crank Fluctuation Sensor) which is NOT found in OBD-1 Civics. Since you are running an OBD-1 ECU, it is not looking for the CKF sensor and therefore is not causing your issue.

How sure are you that your timing belt timing is absolutely correct ? Do you have any codes stored (CEL) ?